Field of the Invention
The present invention relates to a metal-air battery and an energy system.
Description of the Related Art
Metal-air batteries including a metal electrode as an anode and an air electrode as a cathode have been attracting attention as next-generation batteries as having high energy density.
As a representative metal-air battery, a zinc-air battery may be mentioned. FIG. 10 is a schematic cross sectional view for illustrating a discharge reaction of a zinc-air battery. As illustrated in FIG. 10, the zinc-air battery has a structure having a zinc electrode 101 provided in an alkaline electrolytic solution 103 and an air electrode 105 provided on an anion exchange membrane 106 in contact with the electrolytic solution 103, and outputs power from the zinc electrode 101 and the air electrode 105 as a discharge reaction progresses. As the air electrode 105, a cathode catalyst supported on a carbon support is generally used.
In the discharge reaction in the zinc-air battery, metallic zinc from the zinc electrode 101 reacts with hydroxide ions in the alkaline electrolytic solution 103 to be zinc hydroxide, which emits electrons into the zinc electrode 101. The zinc hydroxide decomposes to produce zinc oxide as a precipitate in the electrolytic solution. In the air electrode 105, electrons, water and oxygen react to produce hydroxide ions, which are conducted through the anion exchange membrane 106 to move to the alkaline electrolytic solution 103. As such a discharge reaction progresses, metallic zinc from the zinc electrode 101 is consumed, and zinc oxide will be accumulated in the alkaline electrolytic solution 103. In order to maintain output of power by the zinc-air battery, therefore, it is necessary to supply metallic zinc to the zinc electrode 101 and to remove the zinc oxide precipitate in the alkaline electrolytic solution 103.
To this end, there have been proposed methods for supplying a metal to a metal-air battery (see Japanese Unexamined Patent Publication No. HEI 7 (1995)-45270 and Japanese Unexamined Patent Publication (Translation of PCT Application) No. 2005-509262, for example).
When a metallic compound such as zinc oxide is removed from an electrolytic solution in a conventional metal-air battery, however, the electrolytic solution as well as the metallic compound needs to be drained from an electrolytic tank, and therefore power supply by the metal-air battery needs to be suspended during the removal of the metallic compound.